1. Field
The present invention relates to a robot and a method of controlling the same, and more particularly, to a method of defining control angles to use a limit cycle in order to balance a biped walking robot on a three-dimensional space.
2. Description of the Related Art
In general, machines, which conduct motions similar to those of a human being using an electrical or magnetic action, are known as robots. Early robots were industrial robots, such as manipulators or transfer robots, for work automation and unmanned operation in a production field. These robots performed dangerous work, simple repetitive work, or work requiring large forces, in place of a human being. Recently, biped walking robots, which have a joint system similar to that of a human being, live together with the human being in human working and living spaces, and walk with two feet, have been vigorously researched and developed.
Methods of controlling the walking of a biped robot include a position-based zero moment point (ZMP) control method, and a torque-based finite state machine (FSM) control method. The FSM control method refers to all methods which use a torque control but do not use a ZMP control. In the FSM control method, finite states of the biped robot are defined in advance, and then the finite states of the biped robot are sequentially changed while walking, thus allowing the biped robot to properly walk.
The above FSM-based biped robot uses a limit cycle in order to balance itself on a two-dimensional space. The limit cycle refers to a trajectory movement, which forms a closed loop according to time on the two-dimensional space. When values of a function according to time form a random route in the closed loop as time passes by, the closed loop is referred to as the limit cycle (with reference to FIG. 1).
The limit cycle is divided into stable regions and unstable regions, and performs a nonlinear control. A region of the limit cycle, which is in a regular closed loop range, is referred to as a stable region, and a region of the limit cycle, which is not in the regular closed loop range but diverges radially or converges into one point, is referred to as an unstable region. On the assumption that a biped robot is on a two-dimensional space, control angles are defined by the center of gravity of the biped robot and the foot of the robot contacting the ground and the relationships between the control angles and their differential components, i.e., control angular velocities, are expressed on the two-dimensional space, thus obtaining the limit cycle of FIG. 1. Since the vector of the foot of a biped robot on the two-dimensional space is perpendicular to the ground and the center of the gravity of the biped robot is defined on the two-dimensional space, it is easy to define limit cycle control angles on the two-dimensional space. However, since a biped robot on a three-dimensional space has joints with different positions and directions, it is not easy to define limit cycle control angles of the biped robot on the three-dimensional space. Further, although results of a two-dimensional simulation are combined on a three-dimensional simulation, all data cannot be expressed, and thus in order to balance the biped robot on the three-dimensional space, where the biped robot actually walks, control angles to use the limit cycle should be defined.